Question

Alex only keeps ten pence coins and some twenty pence coins in

his coin box. He has a total of 18 coins which amounts to £2.30.
Work out the number of ten pence coins and twenty pence coins
in Alex's coin box.

Answer 1

In the box. we have 5 20 pence coins and 13 10 pence coins

Explanation:

Let the number of 10 pence coins be x and the number of 20 pence coins be y

The sum of these numbers is 18

Thus;

x + y = 18•••••••(i)

Writing the value in pence only

£2.30 * 100 = 230 pence

Now we have that;

total 10 pence coin amount = 10 * x = 10x

Total 20 pence coin amount = 20 * x = 20y

10x + 20y = 230

x + 2y = 23 •••••••(ii)

from ii;

x = 23-2y

Substitute this into i

23-2y + y = 18

23-18 = 2y-y

y = 5

Recall;

x + y = 18

x + 5 = 18

x = 18-5

x = 13